I asked this question and was told by a national ALPA guy (who I met at random) many years ago that neither the airlines nor our unions want to open up the RLA because it's a can of worms and nobody can predict how it might go down. A push to change it would cross multiple elections and likely a couple WH administrations... the tide could turn at the worst possible moment. His explanation has held up over time.

Even the traditionally "pro labor" politicians don't want catastrophic economic disruption and public (voter) inconvenience, since they would be left holding the bag. Don't believe me? Google (Biden+railroad). Also you have to consider the "Railway" part of the RLA... changes could (would) have even more serious economic and supply chain consequences than just airlines. Assuming the changes end up pro labor to begin with, which is not assured.

I would suggest that anyone proposing RLA amendment needs to specify:

1) What changes they seek, and
2) How they propose to sell (or extort) politicians to get it done, and
3) How they will synchronize it all with the railroad people.

Railroad unions will be very leery, because not only do they need *their* interests accounted for, they don't want a bunch of pilots opening a big can of worms with a lot of possible but not very predictable outcomes... they'll need to feel comfortable that any such attempt would not fall on the wrong side of the fence. As should we.